6i8 



BRAIN MECHANISMS AND LEARNING 



The presence ot the tone at the beginning of the period of darkness, 

 i.e. the flicker-tone association, provoked modifications comparable to 

 the tone-flicker association, but inconstant and less important (Fig. 9). In 



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8 



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11 





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Fig. 9 

 Chaii^Ci ot the I'Isiuil evoked response by effecl of fliiker-toiie iissocicUioii. Stroboscope 

 at 3 m. from the retina. Eyes open. Forty superimposed sweeps. Lead 03-right 

 mastoid, 10/20 system. Arrows indicate the stimulus. Discontinuous flicker 

 frequency 2/sec. during 20 seconds, interrupted during 20 seconds, (i) control 

 without stimulation; (2) habituation to discontinuous flicker frequency after 

 ten trials without association with tone; (3-12) successive trials with flicker 

 (20 seconds) — tone (10 seconds) — darkness (10 seconds) association; (3) ist 

 trial with flicker-tone association, no appreciable modifications with respect 

 to previous trial are noted; (4) 6th trial, the response is considerably increased; 

 (5-7) 7th, 9th and loth trials respectively, response again decreases; (8-1 1) nth, 

 i6th, 21 St and 29th trials respectively, an increase takes place and is maintained; 

 (12) 31st trial, decreases again. Calibration, 200 msec. 



some experiments the central response underwent remarkable changes 

 whereas the occipital one did not show significant variations (Fig. lo). 



The dishabituation obtained by the tone-flicker or flicker-tone associa- 

 tions persisted during various trials when these stimuli were substituted by a 



